Draw a p Chart in Excel
Use p Charts when counting defective items & the sample size varies
The p Chart is one of four attribute control charts used to evaluate the stability of a process over time using counted data. p charts are sometimes confused with u Charts.
Defective Items - p Charts
Each item is only counted once:
- car doors that need to be repainted
- bills that are wrong
- incomplete shipments
Defects - u Charts
Each item can have more than one defect:
- scratches on a car door
- errors on a bill
- missing products in a shipment
p Chart Data Example
Example of a p Chart
Uneven control limits result from the varying sample sizes.
It's Easy to Draw a p Chart in Excel Using QI Macros
QI Macros adds a new menu to Excel and provides two ways to create charts:
What your organization has done with the excel macros is great. It saves me a lot of time by not having to create the formulas and links. Your QI Macro's are better than most SPC specific software on the market. I have been using your macros since 1997.
- Chuck Whitaker
Nishikawa Standard Co.
Create a p Chart by running a macro:
- Select your data.
- Click on QI Macros menu > Control Charts (SPC) > Attribute (c,np,p,u,g,t) > p.
- QI Macros will do the math and draw the chart for you.
- QI Macros will also turn any unstable points or conditions red - these should be investigated.
Create a chart using a p Chart template:
- Open a template: QI Macros > Control Chart Templates > Attribute (c,np,p,u,g,t) > p Chart
- Input your data into the yellow shaded area.
- The chart is drawn as the data is input.
- Run stability analysis using the chart tools menu.
p Chart template options
Learn more about QI Macros control chart template options
- Located to the right of the chart, this functionality allows you to change the multiplier. This automatically changes the y-axis value (e.g. 1, 10, 100, etc.):
- Specifically offered in the p Chart macro, you can toggle between a p Chart and a p' Chart by inputting either "False" (p Chart) or "True" (p' Chart). This option is located to the right of your chart:
If you have created a skyline template and the error bars are not extending, below are instructions on how to update your file accordingly:
- If your template is formatted to Wavy Control Limits, convert them to Skyline Control limits within QI Macros by first selecting your chart. From the QIMacros Chart portion, select the "Convert SkyLine/Wave" drop-down and click "Convert Wave to Skyline."
- Next, click any point on your Upper Control Limit and choose "Format" from the Excel ribbon.
- Then, select "Series UCL X Error Bars" from the Chart Area drop-down:
- Once you have done so, click the "Format Selection" button and then select "Specify Value" from the Format Error Bars section:
- When the "Custom Error Bars" window opens, update the Positive Error Value and Negative Error Value from $M$70 and $T$70 to $M$150 and $T$150 accordingly:
- Repeat these steps for UCL Y Error Bars, LCL X Error Bars, and LCL Y Error Bars.
Why Choose QI Macros Over Other Control Chart Software?
- Only $299 USD - less with quantity discounts
- No annual subscription fees
- Free technical support
Easy to Use
- Works right in Excel
- Create a chart in seconds
- Easy to customize & share charts
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